How to create an AI to solve a word search?
This sounds like a problem that might be solvable with a LSTM-DQN approach, as described in Language Understanding for Text-based Games using Deep
Reinforcement Learning by Narasimhan et al., 2015, and then extended to a domain very similar to your problem in Deep Reinforcement Learning for Syntactic Error Repair in Student Programs by Gupta et al., 2019.

The basic idea is to treat the array of letters each of which can be 'circled' or not, plus the position of a cursor as a state. An action is to move the cursor or toggle the state of a letter. You then model the problem as a reinforcement learning problem, with rewards given every time an entire new word becomes 'circled', probably with a caveat about not circling any invalid letters (otherwise, it'll just learn to circle everything).

This is just a guess, but it seems like it's very closely related to your problem, so it's likely to be effective.